Ion source with space charge neutralization



.J. W. FLOWERS ETAL ION SOURCE WITH SPACE CHARGE NEUTRALIZATION Jan.22', 1953- 2 Sheets-Sheet 1 Filed March 27, 1961 20 NEUTRAL gums/Tons.John W. Flowers. John S. Luce r William 1.. Stirling ATTQRNEY SOURCE WGAS,

C Jan. 22, 1963' J. w. FLOWERS ETAL 3,975,115

ION sow-10s WITH SPACE CHARGE NEUTRALIZATION- Filed March 27, 1961 2Sheets-Sheet 2 Fig. 2.

INVENTOBS. John W, Flowers BY John S. Luce William L. Stir/mg 0v 7 MawATTORNB United States Fascias Q 3,975,115 ION SOURCE WHTH SPACE(Il-IARGE NEUTRALlZATlON John W. Flowers, Gainesville, Fla, .lohn S.Luce, Danville, Calif., and William L. Stirling, Gait Ridge, Tend,assignors to the United States of America as represented by the UnitedStates Atomic Energy (Zommission.

Filed Mar. 27, 196i, Ser. No. 98,726

. 9 Claims. (Cl. 3l3-63) This invention relates to an ion source andmore particularly to an ion source in'which means are provided to insurespace charge neutralization to thus provide an ion beam which isneutralized at all times.

Space charge, neutralization is normally obtained in the prior art byproviding a source of. electrons near the exit of the ion source or bymeans of a neutralvapor to provide a cloud of electrons around the ions.However, it is indeed dllficult to provide the proper amount and spacialdistribution of electrons at all times because of changes in the iondensity. in addition, plasma oscillations will occur due to non-uniformelectron distribution across the ion exit beam. Also, by providingspace-charge neutrali zation at the exit end of the ion source and onlyafter acceleration, complete neutralization does not occur throughoutthe machine. Thus, space charge forces will exist in the machine beforeacceleration so as to limit the ion current and thus the thrust unlesselectrons are provided. The thrust of the neutralized beam is animportant aspect of the ion source of this invention when such a sourceis used in the field of ion propulsion of space vehicles. Unless thespace charge effect is completely new tralized, there 'will bea definitelimit on the thrust ob- I as a result of the space-charge effect, whenintense ion beams are ejected from an ion .source. This difiicultyincludes a limitation of the output as predicted by Lang- .7 muir-Childslaw andprevcnts the formation of a well-' defined beamdue to the wellknown ion beam blow up. In the field of plasma physics, there are manyapplications where a-high current, well-defined ion source is desirable.In addition to the use of such a source in the ion propulsion of spacevehicles as mentioned above, one other specific field for such usageis-the ion injection into machines for producing high density plasmasfor neutron production. Another use for such an ion source is forthe'ion injection into experimental machines to study the feasibility ofcontrolled thermonuclear reactions.

With a knowledge of the limitations of prior art ion sources, asdiscussed above, it is a primary object of this invention to provide. anion beam that is neutralized at all times so that space charge forcescannot develop.

it is a further object of this invention to provide'an ion source withmeans for ejecting a high energy neutralized beam therefrom.

It is another object of this invention to provide an ion source withmeans for ejectinga high density neutral plasma therefrom. I

' It is an additional object of this invention to provide a high.specific impulse arc-ion system for the propulsion of space vehicles.

These and other objects and'advantages of this invention will becomeapparent upon consideration of the following detailed specification andthe accompanying drawings, wherein:

FIG. 1 is a schematic drawing of a neutralized electron-- ion source;

FIG. 2 is a sectional view of an injector device employing the ionsource and electron gun of FIG. 1 for producing an energetic neutralizedbeam of electrons and ions; I

e t smalls 35g Patented'dan. 22, secs FIG. 3 is a sectional view of aninjectordevice em- I ploying the ion source oi,-FlG. l for producinghigh may be used as a variable specific impulse system for.

propulsion of space vehicles; and,

FIG. 5 is a schematic drawing of another embodiment of a variablespecific impulse system for the propulsion of space vehicles. p

The above objects have been accomplished in the present invention byproviding an ion source in which a refluxing type of gas-fed arcdischarge is used to provide ions, and providing an electron gun'fordirecting a controlled, monoenergetic electron beam throughthedischarge. There will be an intimate mixing of the fiCCCIe eratedions and electrons within the ion source and beyond the ion source formore efi'ective space charge ncutralization. I The space chargeneutralization in the ion source and accelerating gap is effected byoscillating, low energy electrons, and the space charge neutralizationof the exit beam from the ion source is effected by the monoenergetic itobviates the possibility of'a net charge developing in the spacevehicle. When a conventional ion source is used in the vehicle, ions maybe attracted back to the vehicle and thus limit or prevent the ions fromtheconventional ion source from being ejected from the source, andvrender such a propulsion system ineffective.

FIG. 1 illustrates one embodiment of an electron-ion source in. whichthe principles of this invention may be carried out. The energeticelectrons for this source are provided by an electron gun now to bedescribed.

A filament cathode 1, which may be either directly or indirectly heated,is axially and magnetically-aligned with 'a hollow anode 2. Gas, argonfor example, is fed from a source 4 and through tubing 3 to the hollowarea of the anode 2. A volt 11C. source 5 is connected between cathode 1andanode 2 by leads 7 and 6, respectively. A gas arc is struck betweenthe cathode 1 and anode 2. This 150 'volt DC. potential is actuallyapplied across the narrow plasma sheath formed by theme plasma at thefilament surface. Thus, the electrons see a very strong electric fieldgradient. This arrangement permits 1 tential. The electron gun ispositioned in a strong, that is,

about 6000 gauss, axial magnetic field provided byelec tromagnets, notshown, so, that the electron stream 11 is well collimated. The directionof the magnetic field is shown by the arrow H. A high-potential shield 8surrounds the electron gun. The shield increases the gas efiiciency ofthe gun and reduces electrical breakdown problems at high acceleratingpotentials. Anaccelcration electrode 19 is provided-just beyond theshield 8, and is electrically connected to the shield 8 by a lead 9. Theshield 8 and electrode 10 are connected to a source of high potential ofabout 39 to 43 kv., negative, with respect to the ion source, to bedescribed below. v

This electron gun will produce a 1 ampere, non- I divergent, 5 kv.electron beam of inch diameter- This mounted within a tubular member 14.The member 14 is provided with flanges on each end. An annularinsulating member 13 is mounted between end plate 12 and the flangeportion at one end of member 14. An annular shield is mounted to andwithin the annular insulator 13 and closely encompasses the hollowcathode 16. The member 14 is provided with an internal, enlarged portionwhich closely encompasses the hollow cathode 16, as shown, forpreventing ions from the arc discharge entering the area occupied by theshield 15. The cathode 16 and anode 17 are axially and magneticallyaligned with the electrodes of the electron gun.

An. annular end plate 20 with a tungsten insert 21 is affixed to theflange portion on the other end of member 14. The plates 12 and 20 areconnected to D.C.

' sources of 99.85-kv. and 100 kv., respectively, not shown.

An annular electrode 22. is positioned beyond the end plate 22. Thiselectrode 22 is insulated'and is thus electrically floating. Gas whichmay be deuterium, for ex-.

ample, is fed from a source 19 and through a tube 18 to the interiorof'the hollow anode 17. A refluxing gas arc discharge 23 is initiatedbetween the cathode 16 and anode 17 in the same manner as set forth inthe US. patent to John S. Luce, No. 2,927,232, issued March 1, 1960,with the exception that gas is not fed to the cathode.

The axial magnetic field of 6000 gauss provided for the electron gun isalso used for the ion source. The electron gun and the ion source areboth enclosed within a chamber, not shown, which is evacuated to apressure of about 3X 10- mm. Hg. The ion source will produce a /2ampere, 6 kv. ion beam using deuterium as the feed gas.

The energetic electron stream 11 from the electron gun is directedthrough the center of the refluxing arc discharge 23. There is anintimate mixing of the accelerated ions and electrons within the ionsource and accelerating gap due to the oscillating electrons within thesource and an intimate mixing of the accelerated ions and electronsbeyond the exit end'of the ion source due to the energetic electronsemerging with'the exit ion beam. Thus, there is effective space chargeneutralization within and beyond the ion source. An accelerationelectrode 24 at ground potential is provided for withdrawing the ionsfrom the source through end plate 20 and electrode 22. Some of theelectrons from the energetic stream 11 of electrons will arrive at theacceleration electrode 24 and have sufiicient energy to pass throughthis electrode along with the ions from the ion source to thus provide aneutralized beam 25 of electrons and ions.v By providing space chargeneutralization within the arc gap, the current output of the beam 25 issubstantially increased above that which is obtained from a conventionalion source because the emission from the conventional ion source islimited by space charge forces.

The insulated electrode 22 is employed as a defining electrode and ithas been found that the use of this electrode also increases the currentoutput of the neutralized beam 25. The relatively cold electrons of thearc dis charge 23 and those of'the energetic beam 11 which are sloweddown by collision processes do not have sufficient energy to passthrough the electrode 24 since this electrode will repel such low energyelectrons which will then oscillate between the electrode 24 and thecathode 16. These oscillating electrons will provide for space chargeneutralization within the ion source and accelerating gap as discussedabove. It should be noted thatthe electrons and ions in the ion sourceare subjected to the same magnetic and electrostatic fields. Bycontrolling the density of all of the electrons, the resultant beamwould be neutralized at all times. Space charge neutralization will takeplace within the ion source in the accelerating gap, and beyond theaccelerating electrode.

The neutralized beam of FIG. 1 may be used in an injector for injectingthe beam into a neutron producing plasma machine. In order to provide ahigh density plasma in such machines, the density of the injected ionsshould be as great as possible, for example, about l0 /cc. at 600 k.e.v.By using the principles of FIG. 1 in such an injector, it is possible toachieve such density which would not otherwise be possible withconventional ion source because the electrostatic force resulting fromspace charge would blow up the beam. FIG. 2 illustrates how the ion.source of FIG; 1 may be used in a neutralized beam injector. An electronsource tube 27 supports an indirectly heated filament 28 which is spacedfrom a hollow anode 29. The electron stream 50 from the electron sourceis directcd through a plurality of annular electromagnetic coils 52, 53,54, 55, and 56, then through the ion source to be described below, thenthrough a. plurality of electromagnetic coils 58, 59, 60, and 61, andthen through a shielded injection tube 49. The ion source is encompassedby an electromagnetic coil 57. The coils 52-61 provide a collimatingmagnetic field whose strength is about 6000 gauss at the coil centersand about 2000 gauss in the gaps between the coils and whose directionis indicated by the arrow H. The device of FIG. 2 is enclosed within avacuum chamber 30. This chamber 30 is formed by the member 31, anannular plate 32, a tubular insulating wall 33, an annular plate 33, atubular plate 63, an annular plate 40, a tubular insulating wall 41, anannular plate 46, and a vacuum manifold 47. The member 31 is connectedto two vaccum pumps 26 and 26; The manifold 47 is connected to twovacuum pumps 48 and 48. The chamber 30 is evacuated by these pumps 26,26', 48, 48 to a pressure of about 3X10 mm. Hg.

The coils 52-56 and 53-61 are enclosed within metallic housings. Thehousings around coils 52 and 53 are connected to zero potential byelectrical leads, not shown. The housings around coils 54, 55 and 56 areconnected through members 34 and 35 and electrical leads, not shown, tosources of DC. potential of kv., 300 ltv., and 450 kv., respectively.The upper and lower plates of the ion source are connected throughmembers 38 and 40, and electrical leads, not shown, respectively, toD.C. sources of 599.85 kv. and 600 kv., respectively. The housingsaround coils 58, 59 and 60 are connected through members 42 and 43. andelectrical leads, not shown, to sources of DC. potential of 450 kv., 300kv., and 150 kv., respectively. The housing around coils 61 is connectedto zero potential by electrical leads, not shown. A shield member 62 ispositioned at the exit end of coil 61 to insure that the electron-ionbeam 51 will enter the injector tube 49.

The potential gradients between the housings of the coils 53-56 willfirst accelerate the electrons from the electron source and thepotential gradients between the housings of coils 58-61 will thendecelerate the electrons after they pass through the ion source. Thepotentialgradicnts between the housings of coils 58-61 will in turnaccelerate the ions from the ion source in such a manner that the ham 51of electrons and ions being ejected from the tube 49 will havesubstantially the same velocity and the beam 51 will be substantiallyspacecharged neutralized. In order to prevent these potential gradientsbetween the coil housings from breaking down the insulating members 33and 41, shield members 36 are provided above the ion source to protectthe member 33, and shield members 44 are provided below the ion sourceto protect the member 41.

The ion source of FIG. 2 includes a hollow cathode 65, a hollow anode66. and an accelerating electrode 64. Gas is fed to the interior ofanode 66 through a feed tube 67. The accelerating electrode 64 isconnected to a source of accelerating potential, not shown, of about 560kv. The electrodes 28, 29, 65, 66, and 64, the coils 52- 56, the coils58-61, and the tube 49 are all in axial alignment on a common axis andthis axis is parallel to the direction of the magnetic field H.

A refluxing arc discharge is established in the ion source of FIG. 2 inthe same manner as set forth for FIG. 1 above. The density of theelectron stream 50 is so cong 79 is affixed to the. plate 91.

' vehicles.

' the electron gun portion of FIG. 4,

trolled as to provide substantially complete space charge neutralizationof the exit beam 51. It should thus be seen that the device of FIG. 2will provide an energetic, neutralized beam of electrons and ions. Theinjector of FIG. 2 is particularly suited for the injection of two ormore molecular ion species into plasma, neutron producing devices. Sincethe beam of HG. 2 is straight throughout the length of the injector,both diatomic and triatomic ions produced in the ion source can beinjected simultaneously into such devices.

It may be desirable to provide a higher density neutralized plasma beaminjector. This may be accomplished by eliminating some of theaccelerating and decelerating stages of FIG. 2 and by using low'eraccelerating and decelerating voltages. Such a device is illustrated inFIG. 3. An electron source tube 85 which supports an indirectly heatedfilament 86 is mounted in an end plate 72. A hollow anode 87 is spacedfrom the filament 36 and is axially aligned therewith. The electron gunprovides an electron beam 74.

The ion source of FIG. 3 includes an annular end plate 91 in which ahollow cathode 82 is supported, a hollow anode 83 to which is fed asource of gas through a feed tube 84, an annular end plate 92, anaccelerating electrode 71, and an electromagnetic coil 89 surroundingthe cathode 82 and anode 83. An electromagnetic coil 38 is mounted tothe plate 72 and encompasses the filament cathode 86 and anode 87 of theelectron gun. The space be ween the coil 88 and end plate 91 isencompassed by an annular shield member 77. An electromagnetic coil 90is spaced from the accelerating electrode 71 and is mounted on an endplate 73. The space between the coil 90-and the plate 92 is encompassedby an annular shield member 76.

The coils 88, 89 and 90 provide a collimating magnetic field whosedirection is indicated by the arrow Hand whose strength is about 6000gauss at coil centers and about 2000 gauss in the gaps between thecoils. The electrodes 86, 37, 82, 33, and 71, and the coils 88, 39, and90 are axially aligned on a common axis and this axis is parallel to thedirection of the magnetic field H.

A member 78 is afiixed to the plate 72 and a member These members 78 and79 are provided with tlange portions, as shown, to provide openingswhich are connected to vacuum pumps, not shown. A member 80 is connectedto plate 92, and a member 81 is connected to plate 73. These members 80and 31 are provided with flange portions, as shown, to provide openingswhich are connected to vacuum pumps, not shown. The area within thedevice of FIG. 3 is evacuated by these pumps to apressure of about 3X10-mm. Hg. The plates 72 and 73 are connected to zero volts by means, notshown. The plates 91 and 92 are connected to sources of about 99.85 kv.and 100 kv., respectively, by means, not shown, and the acceleratingelectrode 71 is connected to a source of about 50 kv. by means, notshown.

The device of FIG. 3 operates in the same manner as the device of FIG.Z'with the exception that much lower accelerating and decelerationpotentials are used. The resultant beam 75 of electrons and ions issubstantially completely spaced charged neutralized and has asubstantially higher density than that produced by the device of FIG. 2.By providing a high density neutral plasma, it will be possible toinject such a plasma across magnetic field lines into devices forproducing high density plasmas for neutron production.

A neutralized electron-ion beam may be used in a variable specificimpulse system for the propulsion of space Such an arrangement isillustrated in FIG. 4. The device of FIG. 4 issimilar to that of FIG. 1with the exception that a different electron gun is employed. In ahollow cathode 98 is mounted in a basemember 97. Gas is fed from asource 95, through a tube 96 and through a passageway in member 97 tothe interior of the cathode 98. A hollow anode 99 is spaced from and inaxial alignment with the cathode 98. A DC. source 100 of about 150 voltsis connected between the cathode 98 and anode 99 by leads 101 and 102,respectively. An axial, collimating magnetic field is provided for thedevice of FIG. 4 by coils, not shown, and the direction of thismagnetiofield is shown by the arrow 1-1. A hollow rcllux arc is 'established between the cathode 98 and anode 99. The ion gun of FIG. 4 willproduce an electron beam 103 of about 3 amperes at 2.5 kv. acceleratingpotential. The acceleration of the electrons from the electron gun isprovided by an accelerating electrode, not shown, in a manner similar tothat set forth for FlG. 1.

In the ion source portion of FIG. 4, a hollow tungsten cathode 109 ismounted in an annular end plate 105. A hollow carbon anode 110 ismounted to and within a tubular member 108. Member 108 has flangeportions at its respective ends. The flange portion at one end of member108 is supported by an insulating member 106 which in turn is suportedby the end plate 105. An annular shield member 107 is mounted to andwithin memher 106. Shield member 107 closely encompasses the cathode109. The flange portion at the other end of member 108 is attached to anannular end plate 113. The plate 113 is provided with an annulartungsten insert 114. An insulated, annular electrode 115 is positionedjust beyond the plate 113. An accelerating electrode 116 isprovidedbeyond the electrode 115 and is connected to zero potential. Gasfrom a source 19' is fed through a tube 112 to the interior of anode110.

A door 104 is provided for covering the annular opening in plate whenthe electron gun is not being used. The electron gun and ion source ofFIG. 4 are enclosed in any suitable enclosure. When the device of thisfigure is being used in a space vehicle, the exit end of the enclosureis connected to regions of negligible atmosphere encountered in outerspace so that the enclosure is thus evacuated to the prevailing pressureencountered in outer space. if the device of FIG. 4 is to he used forother purposes, the enclosure may be evacuated to a pressure of about 3X10 mm. Hg by pumps, not shown, in the same manner that FIG. 1 isevacuated.

The electrodes 98, 99, 109, and are axially aligned on a common axis andthis axis is parallel to the direction of the magnetic field H. Arefluxing arc discharge 111 is initiated in the ion source in the samemanner as set forth in FIG. 1 above. The beam 103 of electrons isdirected hrough this are discharge 111 such that substantially completespace charge neutralization takes place at all points within and beyondthe ion source, to thus provide a space charge neutralized beam 117 ofelectrons and ions in the same manner as set forth for FIG. 1

above. I

The amount of thrust provided by the device of FIG. 4 is directlyrelated to the choice of ions which are fed to the interior of the anode110. With the elimination of space charge efiects by neutralizationthroughout the entire propulsion system, ions in various mass ranges andenergy may be utilized so as to provide a' propulsion engine having avariable specific impulse to provide, in turn, for optimum thrust undervarious conditions. With conventional ion sources, the choice of thepropellant ion is limited and is closely associated with the specificim-.

pulse and space charge equations. By being able to utiobtained by vacuumpumps. Then, by injecting selected ones of these propellant ions intothe test facility by use of the device of FIG. 4, the facility isfurther pumped down by the gettering action of these ions when theycondense at room temperature. Thus, it will be possible to conduct amore thorough study in the laboratory of the basic phenomena associatedwith ion propulsion in space.

Rather than using the ion plasma for direct propulsion, the plasma maybe used to heat a separate neutral gas and eject the heated gas througha noule for achieving propulsion. Such a systemis shown in FIG. 5. Thiswould provide an engine in the lower specific impulse range.

in FIG. the elements 96', 97, 98', and 99 of the electron gun are shown,sincethcy may or may not be used in the device of this figure. When theyare not used, the door 104' is positioned over the annular opening inthe end plate 105', and this door is removed from such opening when theyare used. The flange portion of one end of member 108' is afitxed to anannular insulator 106' which, in turn, is afilxed to end plate 105'. Anannular shield 107' is altered to and within insulator 106'. The flangeportion of the other end of member 108' is aiiixed to the annular endplate 113' which is provided with an annular insert 14'. A nozzle 118 isprovided adjacent to the end plate 113'. A hollow cathode 109' ismounted to end plate 105 and is axially aligned with a hollow anode 120'which is mounted to and within the member 108. The propellant neutralgas is fed from a source 120 and through a tube 112 to the interior ofhollow anode 110'.

A magnetic field of about 6000 gauss, average flux density, is providedby coils, not shown. The direction of this field is indicated by thearrow H and is parallel to the'axis of the cathode 109' and anode 110'.The

device of FIG. 5 is enclosed in any suitable enclosure and the enclosureis wnnected to the regionsoi negligible atmosphere in space when thedevice is used in a space vehicle. A refluxing arc discharge 111' isestablished between the anode 110' and cathode 109' in the same manneras set forth in FlG. l. The propellant gas fed to the anode is heated bythe arc discharge 111' and the heated gas 119 is ejected from the devicethrough the nozzle 118.

The device of FIG. 5 may be operated in the same manner as is the deviceof E16. 4. For example, the door 104 is moved to the same position asthe door 104 of FIG. 4, the ion gun is then actuated the same as in H6.4, gas ions are fed to the anode 110' through the tube 112', and thenozzle 118 is connected to a source of accelerating potential the sameas in FIG. 4.

This invention has been described by way of illustration rather thanlimitation and it should be apparent that this invention is equallyapplicable in fields other than those described.

What is claimed is:

1. A neutralized electron-ion source comprising an elongated enclosureprovided with axial openings at its respective ends, means forestablishing a body of ions along the axis of said enclosure and toprovide space charge neutralization therewithin, an electron gunpositioned in spaced relation to one end of said enclosure, saidelectron gun including a cathode, an anode, means for feeding gas to theinterior or said anode, a high voltage shield encompassing said anodeand cathode and provided with an opening in axial alignment with saidcathode and anode, a source of operating potential connected betweensaid anode and cathode, an electron accelerating electrode spaced fromand in axial alignment with the opening in said shield and with saidanode and said cathode, and a source of acceleration potential connectedto said shield and said accelerating electrode, said cathode, anode andaccelerating electrode being axially aligned with the axis of saidenclosure, means for cstablishing a strong magnetic held having adirection parallel to the axis of said enclosure, said enclosure andelectron gun being enclosed within an evacuated chamher, said electrongun providing an energetic stream of electrons which is directed throughsaid body of ions within said enclosure, and an ion acceleratingelectrode provided with an axial opening along the axis of saidenclosure and being positioned beyond the other end of said enclosure,said electron stream having sufilcient density and energy to providecomplete space charge neutralization beyond said accelerating electrodeto thus provide an energetic, neutralized beam of electrons and ionsbeyond said accelerating electrode.

2. A neutralized electron-ion source comprising an elongated enclosureprovided with axial openings at its respective ends, an elongated,hollow, open-ended cathode mounted in the axial opening in one end ofsaid enclosure, an elongated, hollow, open-ended anode mounted withinsaid enclosure and being spaced from and in axial alignment with saidcathode, a source of feed gas, means for feeding gas from said source tothe interior of said anode, means for establishing and sustaining aspace charge neutralized, refluxing arc discharge within said enclosurebetween and within said cathode and said anode, means for providing acollimating magnetic field having a direction parallel to the axis ofsaid cathode and anode, an electron gun positioned beyond and in axialaligment with the axial opening in said one end of said enclosure, saidelectron gun providing an energetic stream of electrons, means disposedbetween said gun and said cathode for accelerating said stream ofelectrons through said refluxing are discharge, said enclosure andelectron gun being enclosed within an evacuated chamber, and an ionaccelerating electrode provided with an axial opening and beingpositioned beyond and in axial alignment with the axial opening in theother end of said enclosure, said accelerating electrode withdrawingions from said enclosure, said energetic stream of electrons havingsumeient density and energy to provide an energetic, neutralized beam ofelectrons and ions beyond said accelerating electrode.

e 3. A neutralized electron-ion source comprising an elongated enclosureprovided with axial openings in each of its ends, means for establishinga body of space charged neutralized ions along the axis of saidenclosure, an electron gun positioned beyond one end of said enclosureand in axial alignment with the axis of said enclosure, said electrongun providing a stream of electrons, means disposed between said gun andsaid enclosure for accelerating said stream of electrons through saidbody of ions within said enclosure, means for providing a uniformcollimating magnetic field along the axis of said enclosure and saidelectron gun, said enclosure and electron gun being enclosed within anevacuated chamber, and an ion accelerating electrode disposed beyond theother end of said enclosure for withdrawing and accelerating ions fromsaid enclosure, said electron stream having sufficient energy to passthrough said ion acceleration electrode to thus provide an energetic,neutralized beam of electrons and ions beyond said acceleratingelectrode.

4. The electron-ion source set forth in claim 3 and further includingadditional means positioned beyond said accelerating electrode forfurther accelerating the ions withdrawn from said enclosure, saidadditional means decelerating the energetic electrons in said electronstream such that the emerging electron-ion beam is neutralized and isprovided with electrons and ions having substantially the same relativevelocity.

5. The electron-ion source set forth in claim 4, wherein theaccelerating means disposed between said electron gun and said enclosureincludes first several stages of accleration, and said additional meansbeyond said accelerating electrode includes second several stages ofaccleration for the ions withdrawn from said enclosure, saidacceleration electrode and said second several stages also providingdeceleration for the electrons in said stream of electrons after theyleave said enclosure.

6. The electron-ion source of claim 4, wherein said accelerating meansdisposed between said electron gun and said enclosure accelerate theelectrons from said electron gun to an energy of about 99.85 ltv., andsaid ion accelerating electrode and said additional means acceleratingsaid ions to an energy of about lO0J v., said ion acceleration electrodeand said'additional means also serving as a means for decelerating saidenergetic electrons after they leave said enclosure.

7. The electron-ion source of claim 5, wherein said first several stagesof acceleration accelerate said electrons from said ion gun to an energyof about $99.85 kv. before they enter said enclosure, and said ionacceleration electrode and said second several stages of accelerationfor said ions accelerate said ions to an energy of about 600 kv.

8. A neutralized electron-ion source device for providing a variablethrust for the propulsion of. a space vehicle comprising an elongatedenclosure provided with axial openings in each of its ends, means forestablishing a refiuxing; space charge neutralized, gas-fed arcdischarge along the axis of and within said enclosure and in alignmen twith said openings, an electron gun positioned beyond one 'end of saidenclosure and in axial alignment with the axis of said enclosure, saidelectron gun providing a stream of electrons, means for providing acollimating magnetic field, said field having a direction parallel tothe axis of said gun and enclosure, said gun and said enclosure beingenclosed within a chamber which is mounted within said vehicle, saidchamber being in communication with regions of negligible atmospherewhich is encountered in outer space. means for accelerating electronsfrom said electron gun through said are discharge, and an ionaccelerating electrode positioned beyond the other end of said enclosurefor withdrawing and accelerating ions from said enclosure, saidelectrons having sufficient density and energy to pass through said ionacceleration electrode to thus provide an elected. energetic,neutralized beam of electrons and ions beyond said accelerationelectrode, the specific thrust to said vehicleprovided by said ejectedbeam being directly related to the type of selected gas fed to said aredischarge. 1

9. The device set forth in claim 8, wherein said electron gun isdisabled, a door being placed over the axial opening in said one end ofsaid enclosure, said accelerating electrode being replaced by a nozzle.and the gas fed to said discharge is a neutral gas, whereby the saiddischarge heat said neutral gas which is then ejected-through saidnozzle to provide a specific thrust to said vehicle as a function of thetype of selected neutral gas fed to said discharge.

References Cited in the file of this patent UNITED STATES PATENTS2,969,308 Bell et al. Jan. 24, 1961

1. A NEUTRALIZED ELECTRON-ION SOURCE COMPRISING AN ELONGATED ENCLOSUREPROVIDED WITH AXIAL OPENINGS AT ITS RESPECTIVE ENDS, MEANS FORESTABLISHING A BODY OF IONS ALONG THE AXIS OF SAID ENCLOSURE AND TOPROVIDE SPACE CHARGE NEUTRALIZATION THEREWITHIN, AN ELECTRON GUNPOSITIONED IN SPACED RELATION TO ONE END OF SAID ENCLOSURE, SAIDELECTRON GUN INCLUDING A CATHODE, AN ANODE, MEANS FOR FEEDING GAS TO THEINTERIOR OF SAID ANODE, A HIGH VOLTAGE SHIELD ENCOMPASSING SAID ANODEAND CATHODE AND PROVIDED WITH AN OPENING IN AXIAL ALIGNMENT WITH SAIDCATHODE AND ANODE, A SOURCE OF OPERATING POTENTIAL CONNECTED BETWEENSAID ANODE AND CATHODE, AN ELECTRON ACCELERATING ELECTRODE SPACED FROMAND IN AXIAL ALIGNMENT WITH THE OPENING IN SAID SHIELD AND WITH SAIDANODE AND SAID CATHODE, AND A SOURCE OF ACCELERATION POTENTIAL CONNECTEDTO SAID SHIELD AND SAID ACCELERATING ELECTRODE, SAID CATHODE, ANODE ANDACCELERATING ELECTRODE BEING AXIALLY ALIGNED WITH THE AXIS OF SAIDENCLOSURE, MEANS FOR ESTABLISHING A STRONG MAGNETIC FIELD HAVING ADIRECTION PARALLEL TO THE AXIS OF SAID ENCLOSURE, SAID ENCLOSURE ANDELECTRON GUN BEING ENCLOSED WITHIN AN EVACUATED CHAMBER, SAID ELECTRONGUN PROVIDING AN ENERGETIC STREAM OF ELECTRONS WHICH IS DIRECTED THROUGHSAID BODY OF IONS WITHIN SAID ENCLOSURE, AND AN ION ACCELERATINGELECTRODE